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Modelling of the effects of laser modification of gas-nitrided layer

Kulka M., Panfil D., Michalski J., Wach P.

Archives of Materials Science and Engineering

2017

Vol. 88, nr 2

59--67

Purpose: The effects of laser processing parameters on the dimensions of simple laser tracks, produced on the previously nitrided layer, were analysed. Design/methodology/approach: Gas nitriding is one of the most commonly used thermochemical treatment, resulting in many advantageous properties: high hardness, enhanced corrosion resistance, improved wear resistance and fatigue strength. However, an unfavourable increase in the thickness of compound zone (e + ɣ’) close to the surface was observed after conventional gas nitriding. This was the reason for undesirable embrittlement and flaking of the layer. Therefore, a controlled gas nitriding was intensively developed, reducing the percentage of the most brittle e (Fe2-3N) iron nitrides. In this study, the hybrid surface layer was produced. The controlled gas-nitriding was followed by laser heat treatment (LHT). Laser modification was carried out using various laser beam powers and scanning rates. The dimensions of laser tracks (i.e. depths and widths of re-melted zone and heat-affected zone) were measured. Numerical methods were used in order to formulate a mathematical model. Findings: Laser processing parameters (laser beam power and scanning rate) influenced the microstructure obtained. The microstructure of laser modified nitrided steel with re-melting consisted of re-melted zone (MZ), heat-affected zone (HAZ), nitrided layer without visible effects of laser treatment and the substrate. The use of laser beam power of 0.26 kW resulted in only a partial re-melting of the compound zone. The two characteristic values of laser beam power were estimated. P0MZ corresponded to the laser beam power at which the re-melted zone disappeared (i.e. width and depth of MZ were equal to 0). P0HAZ was a value of laser beam power at which the effects of laser irradiation were invisible in microstructure (i.e. width and depth of HAZ were equal to 0). The model was proposed in order to predict the effects of LHT on microstructure. Research limitations/implications: The presented model was limited to the scanning rates in the range of 2.24-3.84 m/min. In the future research, this range should be exceeded, especially, taking into account the lower values of scanning rate. Practical implications: The presented model could be used in order to control the microstructure and properties of hybrid surface layers, obtained as a consequence of the controlled gas-nitriding and LHT. Originality/value: his work is related to the new conception of laser modification of nitrided layers. Such a treatment provided the hybrid layers of new advantageous properties.

Microstructure of laser hardened steels.

Barbacki A.

Inżynieria Materiałowa

2001

R. XXII, nr 4

204-207

W artykule przedstawiono wyniki badań za pomocą mikroskopu świetlnego oraz elektronowego mikroskopu skaningowego struktury dwóch stali hartowanych laserowo. Analizowano zarówno makrostrukturę obserwowaną przy powiększeniach do 50x, jak też mikrostrukturę - przy powiększeniach przekraczających 1000x. Badania makroskopowe odzwierciedlają wzajemne położenie sąsiednich przejść lasera oraz głębokość zmian struktury. Badania mikroskopowe pokazały szczegółowo strukturę uzyskaną w warstwie wierzchniej w wyniku zachodzących przemian fazowych.

The results of structure investigation of two laser hardened steels by means of light and scanning electron microscopy are presented in the paper. Both the macrostructure, observed at magnification up to 50x and the microstructure, seen at magnification above 1000x, have been analyzed. The macroscopic investigation reveals mutual arrangement of neighboring laser tracks and the depth of structure changes. The microscopic investigation shows further details of the microstructure and provides information about phase transformations occuring in the surface layer.